This invention relates to underwater acoustic transducer arrays, and more particularly to the structural features thereof which decouple undesired vibrations borne by the structure to which the array is mounted.
In most sonar systems it is important that the lowest receive level be limited by a physical phenomenon beyond man's control at that particular time and state-of-the-art. For torpedoes moving through the water at high speed, the natural generation of noise by water flowing over the face of the transducer should be a limiting level.
Prior efforts in decoupling vibrational noises borne by the support structure were principally aimed at reducing the effect of element to element mutual coupling caused by the support structure during projection of acoustic energy from the transducer in its transmit mode. These efforts are illustrated by U.S. Pat. Nos. 3,492,633 and 3,492,634 to F. Massa. Prior to the present invention it was generally assumed that the noise appearing in the output of the transducers was induced by water flowing across the frontal face of the acoustic window over the array, or if caused by vibration induced in the shell, that the energy was coupled to the transducer by a water path. Not until the tests of the present invention was it recognized that decoupling of an additional order of magnitude beyond that necessary to provide isolation of transducer elements in the transmit mode is desirable.